Reactive sputtering of silicon and transition metal

ABSTRACT

Low absorbance coatings of silicon-nickel alloy in the form of oxides, nitrides and oxynitrides are disclosed along with a method for producing them by sputtering silicon-nickel targets comprising 3 to 18 weight percent nickel in atmospheres comprising reactive gases such as nitrogen, oxygen and mixtures thereof which may further comprise inert gas such as argon. The presence of nickel in the range of 3 to 18 weight percent provides target stability and enhanced sputtering rates over target of silicon alone or alloyed with aluminum, while maintaining a low refractive index and low absorbance, not only when sputtering in oxygen to produce an oxide coating, but also when sputtering in nitrogen or a mixture of nitrogen and oxygen to produce coatings of silicon-nickel nitride or oxynitride respectively.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.07/799,806 filed Nov. 29, 1991, by Finley et al. entitled "MultilayerHeat Processable Vacuum Coatings With Metallic Properties".

BACKGROUND

The present invention relates generally to the art of sputteringsilicon-containing target materials in a reactive atmosphere, and moreparticularly to reactive sputtering of silicon targets furthercomprising a transition metal.

German Patent Application DE 3,906,453 Al to Szczybowski et al.discloses sputtering silicides, such as nickel silicide (NiSi₂), in anoxidizing atmosphere to deposit dielectric oxide films.

The present invention involves silicon-nickel alloys ranging from 3 to18 weight percent nickel. Targets of silicon-nickel alloys are sputteredin an atmosphere comprising nitrogen, oxygen, inert gases and mixturesthereof to produce silicon-nickel containing coatings including oxides,nitrides and oxynitrides. The silicon-nickel compositions of the presentinvention comprise sufficient nickel to provide target stability and adesirable sputtering rate while keeping the absorption of the resultingfilms relatively low.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates the extinction coefficient (k) at 560 nanometers offilms comprising silicon and nickel, sputtered from a silicon targetcontaining 10 weight percent nickel, as a function of the reactive gascomposition over the range from 100 percent nitrogen to 60 percentnitrogen/40 percent oxygen, where the percent oxygen is based on thecombined flows of oxygen and nitrogen in standard cubic centimeters perminute (sccm).

FIG. 2 illustrates the refractive index (n) at 560 nanometers of filmscomprising silicon and nickel, sputtered from a silicon targetcontaining 10 weight percent nickel, as a function of the reactive gascomposition over the range of from 100 percent nitrogen to 60 percentnitrogen/40 percent oxygen.

FIG. 3 illustrates the extinction coefficient (k) at 560 nanometers offilms comprising silicon and nickel, sputtered in an atmosphere of 100percent nitrogen, as a function of nickel content in the silicon targetover the range of 5 to 19 weight percent nickel.

FIG. 4 illustrates the extinction coefficient (k) at 560 nanometers offilms comprising silicon and nickel, sputtered in an atmosphere of 100percent nitrogen, as a function of nickel content in the film, over therange of about 4.7 to 16 weight percent nickel.

FIG. 5 illustrates the sputtering rate, in Angstroms per kilowatt-passat a line speed of 120 inches per minute for films comprising siliconand nickel, sputtered from a silicon target containing 10 weight percentnickel, as a function of the reactive gas composition over the range of100 percent nitrogen to 60 percent nitrogen/40 percent oxygen.

FIG. 6 illustrates the cathode voltage as a function of percent oxygenin an atmosphere comprising from 100 percent nitrogen to 60 percentnitrogen/40 percent oxygen for sputtering a silicon target containing 10weight percent nickel at 3 kilowatts.

FIG. 7 illustrates the percent nickel in films comprising silicon andnickel, sputtered from a silicon target containing 10 weight percentnickel, as a function of the reactive gas composition over the range of100 percent nitrogen to 60 percent nitrogen/40 percent oxygen.

FIG. 8 illustrates the transmittance (%) at 550 nanometers as a functionof film thickness for films sputtered from a silicon target containing10 weight percent nickel in reactive gas atmospheres ranging from 100percent nitrogen to 60 percent nitrogen/40 percent oxygen.

In accordance with the present invention, silicon-nickel oxides,nitrides and oxynitrides are sputtered using D.C. magnetron sputtering.For this purpose, cast silicon-nickel targets are used for thesputtering targets. The sputtering rate is measured for varying amountsof nickel using pure nitrogen, nitrogen-oxygen or oxygen-argon mixturesas the sputtering gas. Optical properties are measured and compared.

The silicon-nickel targets of the invention are found to sputter withless arcing and at higher rates than silicon-aluminum targets. However,when sputtering silicon-nickel with high nickel content, such as nickelsilicide, in nitrogen to form silicon-nickel nitride, the absorption istoo high for certain applications. Since it is desirable in a productionprocess to use the same target material for many coating applicationsand vary the reactive gas to sputter different compositions, the nickelcontent in accordance with the present invention is kept low enough tolimit absorption, particularly when sputtering the nitride compound, buthigh enough to give the desirable sputtering rate and target stability.

Silicon-nickel alloys ranging between 3 and 18 weight percent nickel aresputtered in nitrogen-oxygen gas mixtures ranging from 0 to 40 percentoxygen. These nitrides and oxynitrides have low absorption, whereasalloys with a nickel content of 50 weight percent are found to be highlyabsorbing and consequently of limited utility in a commercial process.

The target compositions are measured by sputtering the targets in argonand using X-ray fluorescence to determine the weight percent nickel. Thetarget compositions may also be determined by the DCP method wheregrindings from the target surface are analyzed. These DCP values confirmthe results obtained by X-ray fluorescence but are a bit higher in somecases due to variation in the target material.

FIG. 1 illustrates that the absorption is low for oxide coatingsdeposited in oxygen-rich atmospheres, but there is a steep increase inabsorption as the nitrogen flow rate increases and the nitride contentof the coating increases. For compositions more than 19 weight percentnickel, the absorption increases more steeply. At 50 weight percentnickel, the absorption k is 0.3 (not shown) which is almost 10 times theabsorption at 20 weight percent nickel. FIG. 2 illustrates a similareffect with respect to refractive index.

FIGS. 3 and 4 illustrate absorption as a function of target and filmcompositions respectively. The absorption for a target or coatingcomprising 50 weight percent nickel (not shown) would be off this scale,which illustrates the effect of nickel content in the film, and why itis necessary to limit the nickel content because of the absorption.Silicon alloy targets containing 3 to 18 weight percent nickel areuseful in accordance with the present invention, with nickel contents of5 to 16 percent being preferred, especially in the range of 7 to 15percent. A 15 weight percent nickel composition is preferred for ease oftarget fabrication. However, lower nickel content is preferred todecrease the absorption, so long as sputtering stability and rates arenot detrimentally affected. Most preferred is a target composition of 3to 10 weight percent nickel. Generally, the weight percent nickel in thefilm, based on the total combined weight of silicon and nickel in thefilm, is somewhat lower than the weight percent nickel in the target asmeasured by X-ray fluorescence and illustrated in FIG. 7.

FIG. 5 illustrates the sputtering rate for the silicon-nickel alloy (10weight percent nickel) used to produce films, the n and k of which areillustrated in FIGS. 1 and 2.

The cathode voltage as a function of percent oxygen in thenitrogen-oxygen gas mixture is shown in FIG. 6 for 10 weight percentnickel targets. FIG. 7 shows the weight percent nickel in the sputteredfilm for the same range of nitrogen-oxygen gas mixtures. FIG. 8 showsthe transmittance as a function of thickness of the coating. The curvesrepresent transmittance for nitrogen and nitrogen-oxygen gas mixtures,and each point on the curve represents the first, third, etc. passduring deposition. The transmittance is monitored at 550 nanometers.

The sputtering rate increases as the oxygen flow rate increases,reaching a maximum rate between approximately 15 and 20 percent oxygen.FIG. 1 of extinction coefficient as a function of percent oxygen showsthat for oxygen greater than 19%, the absorption for the films sputteredfrom the 10 percent nickel target is less than about 0.002. Thisindicates that maximum rate and low absorption are achieved forsputtering in a nitrogen-oxygen gas mixture of 20 to 30 percent oxygen.The refractive index shows a slight increase with nickel content in FIG.2 in the same range. When sputtering in pure nitrogen, or anitrogen-oxygen gas mixture of 20 percent or less oxygen, the absorptionincreases with nickel content. The curve shown in FIG. 3 illustrates theincrease in extinction coefficient as the weight percent of nickel inthe target is increased up to 19 weight percent. The same is shown inFIG. 4 for film composition.

In a preferred embodiment of the present invention, coatings areproduced on a large-scale magnetron sputtering device capable of coatingglass up to 100×144 inches (2.54×3.66 meters). In the followingexamples, the coatings are deposited on a smaller scale, using planarmagnetron cathodes having 5×17 inch (12.7×43.2 centimeters)silicon-nickel targets. Base pressure is in the 10⁻⁶ Torr range. Thecoatings are made by first admitting the sputtering gas to a pressure of4 millitorr and then setting the cathode at constant power of 3kilowatts (kw). In each example, 6 millimeter thick glass substratespass under the target on a conveyor roll at a speed of 120 inches (3.05meters) per minute. The transmittance is monitored every other passduring the sputtering process at a wavelength of 550 nanometers using aDyn-Optics 580D optical monitor.

After the coating is deposited, the transmittance and reflectance fromboth the glass and coated surface are measured in the wavelength rangefrom 380 to 720 nanometers using a Pacific Scientific Spectrogard ColorSystem spectrophotometer. These data are used to calculate the coatingrefractive index n and absorption coefficient k shown in the figures for560 nanometers. The thicknesses of the coatings are measured usingTencor P-1 Long Scan Profiler.

EXAMPLE 1

A sample is prepared using a silicon-nickel (10 weight percent) targetin a pure nitrogen gas atmosphere with a flow of 103 standard cubiccentimeter per minute (sccm). The cathode voltage is 478 volts. Thesputtered film deposited in this nitrogen-oxygen gas mixture is 6.7weight percent nickel based on the total weight of silicon and nickel inthe film. The transmittance of the coating, monitored at 550 nanometers,is 80.0 percent after 8 passes. The coating thickness is 490 Angstroms,and the sputtering rate is 20.4 Å/kw-pass. The index of refraction (n)is 2.02, and the extinction coefficient (k) is 0.0250 at 560 nanometers.

EXAMPLE 2

A sample is prepared using a silicon-nickel (10 weight percent) targetin a nitrogen-oxygen gas mixture with an oxygen flow of 6 sccm and anitrogen flow of 99 sccm. The cathode voltage is 493 volts. The weightpercent nickel in the sputtered film is 7.3 based on the combined weightof silicon and nickel in the film. The transmittance of the coating,monitored at 550 nanometers, is 83.9 percent after 14 passes. Thecoating thickness is 936 Angstroms, and the sputtering rate is 22.3Å/kw-pass. The index of refraction (n) is 1.78, and the extinctioncoefficient (k) is 0.0089 at 560 nanometers.

EXAMPLE 3

A sample is prepared using a silicon-nickel (10 weight percent) targetin a nitrogen-oxygen gas mixture with an oxygen flow of 11 sccm and anitrogen flow of 98 sccm. The cathode voltage is 503 volts. The weightpercent nickel in the sputtered film is 7.6 based on the total weight ofsilicon and nickel in the film. The transmittance of the coating,monitored at 550 nanometers, is 87.6 percent after 15 passes. Thecoating thickness is 1061 Angstroms, and the sputtering rate is 23.6Å/kw-pass. The index of refraction (n) is 1.66, and the extinctioncoefficient (k) is 0.0059 at 560 nanometers.

EXAMPLE 4

A sample is prepared using a silicon-nickel (10 weight percent) targetin a nitrogen-oxygen gas mixture with an oxygen flow of 16 sccm and anitrogen flow of 92 sccm. The cathode voltage is 474 volts. The weightpercent nickel in the sputtered film is 7.5 based on the total weight ofsilicon and nickel in the film. The transmittance of the coating,monitored at 550 nanometers, is 91.3 percent after 15 passes. Thecoating thickness is 1213 Angstroms, and the sputtering rate is 27Å/kw-pass. The index of refraction (n) is 1.52, and the extinctioncoefficient (k) is 0.0027 at 560 nanometers.

EXAMPLE 5

A sample is prepared using a silicon-nickel (10 weight percent) targetin a nitrogen-oxygen gas mixture with an oxygen flow of 21 sccm and anitrogen flow of 84 sccm. The cathode voltage is 423 volts. The weightpercent nickel in the sputtered film is 6.5 based on the total weight ofsilicon and nickel in the film. The transmittance of the coating,monitored at 550 nanometers, is 91.9 percent after 19 passes. Thecoating thickness is 1460 Angstroms, and the sputtering rate is 25.6Å/kw-pass. The index of refraction (n) is 1.48, and the extinctioncoefficient (k) is 0.0017 at 560 nanometers.

EXAMPLE 6

A sample is prepared using a silicon-nickel (10 weight percent) targetin a nitrogen-oxygen gas mixture with an oxygen flow of 25 sccm and anitrogen flow of 75 sccm. The cathode voltage is 380 volts. The weightpercent nickel in the sputtered film is 5.2 based on the combined weightof silicon and nickel in the film. The transmittance of the coating,monitored at 550 nanometers, is 92.3 percent after 19 passes. Thecoating thickness is 1111 Angstroms, and the sputtering rate is 19.5Å/kw-pass. The index of refraction (n) is 1.48, and the extinctioncoefficient (k) is 0.0015 at 560 nanometers.

EXAMPLE 7

A sample is prepared using a silicon-nickel (10 weight percent) targetin a nitrogen-oxygen gas mixture with an oxygen flow of 30 sccm and anitrogen flow of 70 sccm. The cathode voltage is 371 volts. The weightpercent nickel in the sputtered film is 4.4 based on the total weight ofsilicon and nickel in the film. The transmittance of the coating,monitored at 550 nanometers, is 92.3 percent after 17 passes. Thecoating thickness is 1007 Angstroms, and the sputtering rate is 19.7Å/kw-pass. The index of refraction (n) is 1.48, and the extinctioncoefficient (k) is 0.0020 at 560 nanometers.

EXAMPLE 8

A sample is prepared using a silicon-nickel (10 weight percent) targetin a nitrogen-oxygen gas mixture with an oxygen flow of 38 sccm and anitrogen flow of 56 sccm. The cathode voltage is 360 volts. The weightpercent nickel in the sputtered film is 4.2 based on the total weight ofsilicon and nickel in the film. The transmittance of the coating,monitored at 550 nanometers, is 92.3 percent after 19 passes. Thecoating thickness is 987 Angstroms, and the sputtering rate is 14.3Å/kw-pass. The index of refraction (n) is 1.48, and the extinctioncoefficient (k) is 0.0022 at 560 nanometers.

EXAMPLE 9

A sample is prepared using a silicon-nickel (15 weight percent) targetin a pure nitrogen gas atmosphere with a flow of 106 sccm. The cathodevoltage is 499 volts. The weight percent nickel in the sputtered film is12.4 based on the total weight of silicon and nickel in the film. Thetransmittance of the coating, monitored at 550 nanometers, is 82.6percent after 5 passes. The coating thickness is 297 Angstroms, and thesputtering rate is 19.8 Å/kw-pass. The index of refraction (n) is 1.99,and the extinction coefficient (k) is 0.0283 at 560 nanometers.

EXAMPLE 10

A sample is prepared using a silicon-nickel (19 weight percent) targetin a pure nitrogen gas atmosphere with a flow of 101 sccm. The cathodevoltage is 487 volts. The weight percent nickel in the sputtered film is15.6 based on the combined weight of silicon and nickel in the film. Thetransmittance of the coating, monitored at 550 nanometers, is 72.8percent after 8 passes. The coating thickness is 496 Angstroms, and thesputtering rate is 20.7 Å/kw-pass. The index of refraction (n) is 2.04,and the extinction coefficient (k) is 0.0443 at 560 nanometers.

EXAMPLE 11

A sample is prepared using a silicon-nickel (15 weight percent) targetin an oxygen-argon gas mixture with an oxygen flow of 55 sccm and anargon flow of 55 sccm. The cathode voltage is 325 volts. The weightpercent nickel in the sputtered film is 5.8 based on the total weight ofsilicon and nickel. The transmittance of the coating, monitored at 550nanometers, is 91.6 percent after 12 passes. The coating thickness is703 Angstroms, and the sputtering rate is 19.5 Å/kw-pass. The index ofrefraction (n) is 1.48, and the extinction coefficient (k) is 0.0007 at560 nanometers.

EXAMPLE 12

A sample is prepared using a silicon-nickel (5 weight percent) target ina pure nitrogen gas atmosphere with a flow of 99 sccm. The cathodevoltage is 547 volts. The weight percent nickel in the sputtered film is4.7 based on the total weight of silicon and nickel in the film. Thetransmittance of the coating, monitored at 550 nanometers, is 76.6percent after 11 passes. The coating thickness is 548 Angstroms, and thesputtering rate is 16.6 Å/kw-pass. The index of refraction (n) is 1.98,and the extinction coefficient (k) is 0.0123 at 560 nanometers.

EXAMPLE 13

A coating comprising silicon nickel nitride is prepared by employing acommercial coater using all planar magnetron cathodes. Solargray® glassof thickness 4.0 mm is coated in block sizes of 23×42 inches (0.58×1.1meters) and 22×59 inches (0.56×1.5 meters) arranged in a covey of either84×144 inches (2.1×3.7 meters) or 100×144 inches (2.5×3.7 meters). Theglass is sputter coated first with titanium in inert argon atmosphere,then titanium in nitrogen atmosphere, then silicon-nickel (15 weightpercent) in nitrogen to form a coated glass article wherein the coatingcomprises titanium/titanium nitride/silicon-nickel nitride. The coatedglass may be washed, cut, edged, screen printed with a black band andtempered for use as an automotive transparency for privacy glazing. Thecoating thicknesses for the individual layers are in the range of 25Angstroms titanium, 430 Angstroms titanium nitride and 300 Angstromssilicon-nickel nitride. Typical optical properties of these coated glassarticles before and after heating are the following:

    ______________________________________                                                     UNHEATED HEATED                                                  ______________________________________                                        Film Side                                                                       Y 12.8 10.2                                                                   x .369 .330                                                                   y .389 .355                                                                   TSER 24.5 25.4                                                                Glass Side                                                                    Y 13.0 10.7                                                                   x .310 .298                                                                   y .335 .323                                                                   TSER 14.0 13.0                                                                Transmittance                                                                 LTA 14.8 20.0                                                                 TSET 10.7 13.0                                                              ______________________________________                                    

The color and reflectance are measured on a Spectrogard Color Systemspectrophotometer.

The above examples were prepared using silicon-nickel targets sputteredin pure nitrogen, in nitrogen-oxygen gas mixtures ranging from up to 40percent oxygen, and in an argon-oxygen mixture comprising 50 percentoxygen. Based on the data illustrated in the figures, a singlesilicon-nickel sputtering target containing a low weight percentage ofnickel can be used for stable sputtering of a range of film compositionsincluding oxides, nitrides and oxynitrides with low absorption at highsputtering rates. The above examples illustrate the concept of thepresent invention, the scope of which is defined by the followingclaims.

What is claimed is:
 1. A coated article comprising:a. a nonmetallicsubstrate; and b. a coating comprising silicon and nickel wherein theweight percent nickel based on the combined weight of silicon and nickelis from 3 to 18 percent.
 2. A coated article according to claim 1,wherein the nonmetallic substrate is transparent.
 3. A coated articleaccording to claim 2, wherein the substrate is glass.
 4. A coatedarticle according to claim 3, wherein the weight percent nickel is from5 to 16 percent.
 5. A coated article according to claim 4, wherein theweight percent nickel is from 7 to 15 percent.
 6. A coated articleaccording to claim 5, wherein the coating further comprises an elementselected from the group consisting of oxygen, nitrogen and mixturesthereof.
 7. A coated article according to claim 6, wherein theextinction coefficient of the coated article is less than 0.05.
 8. Acoated article according to claim 7, wherein the coating issilicon-nickel nitride.
 9. A coated article according to claim 7,wherein the coating is silicon-nickel oxynitride.
 10. A coated articleaccording to claim 7, wherein the coating thickness is from 50 to 2000Angstroms.
 11. A coated article according to claim 1 wherein the coatingis deposited on the substrate.
 12. A coated article according to claim 1wherein the coating is defined as a top coating and further including afunctional coating between the top coating and the substrate.
 13. Acoating accoeding to claim 12 wherein the substrate is glass.